The objective of the proposed research is to isolate, characterize, and understand the human genes involved in heritable cardiac conduction disease. Identification of these genes will enhance our understanding of the molecular mechanisms of cardiac conduction and may play a significant role in the development of new diagnostic and therapeutic modalities for cardiac arrhythmias. Specifically, this proposal will focus on the clinically heterogeneous inherited cardiac conduction disorder, long QT syndrome (LQT). Affected individuals have an pathognomic electrocardiographic abnormalities such as an abnormal prolongation of the QT interval with asymmetric or noted T or U waves. We have characterized two large multi-generational families with this syndrome which predisposes affected members to seizures, recurrent fainting, and sudden death at an early age from ventricular tachyarrhythmias. We are currently identifying other families with LQT. The goal of this research proposal is to isolate and characterize the gene locus (loci) responsible for LQT. To date, our understanding of the molecular and cellular phenotype of LQT is limited, though it is believed to be a molecular defect in cardiac muscle cell excitability. Recently, genetic linkage analysis has been performed in a family with LQT(1). A DNA marker at the Harvey ras-1 locus (H-ras-1) has been linked to LQT in this family. This finding confirms the genetic basis of this trait and localizes the responsible gene to the vicinity of the H-ras-1 gene on the short arm of chromosome 11. Physiological data demonstrates that the product of the H-ras-1 gene, p21 ras protein, regulates cardiac potassium channels(2). Thus, based on its physiologic role in modulating cardiac ion transport, that ras is a reasonable candidate for the abnormal gene responsible for LQT. However, it is important to note that even though linkage has been established for this family to H-ras-1 locus, it has not been demonstrated that H-ras-1 is the disease gene. Through the identification and characterization of new families with LQT, the establishment of genomic DNA bank derived from lymphoblastoid cell lines of family members, and genetic linkage analysis studies with H-ras-1 markers and other newly developed DNA markers, we will demonstrate if these families are linked to H-ras-1 gene locus. Based on these results, further studies using SSCP analysis, yeast artificial chromosome libraries and CA polymorphisms will be designed to either evaluate ras, the region near ras or another newly defined locus. The purpose of this research proposal is to determine whether H-ras-1 gene is responsible for LQT in these families. If the H-ras-1 gene is not responsible, then we will identify the responsible gene. Our ultimate aim is to structurally and functionally characterize the gene so that we can better understand the molecular mechanism of disease.